Conventionally, an operation device having a rotationally operated operation knob is provided to an instrumental panel and the like of an automobile. Rotating the operation knob changes a rotation amount of a rotary encoder and the like. According to the rotation amount, an operation object, such as air conditioner temperature and audio instrument volume, is controlled. In some cases, such an operation device is provided with an illumination light source in order to illuminate an operation knob or the like.
For example, Patent Literature 1 discloses an operation device B10 that changes and controls air conditioner temperature, as shown in FIGS. 5 and 6. The operation device B10 includes a rotary encoder B50, a fixed display B60 having a circular plate shape, an operation knob B30, an illumination light source B40, and a light guiding body B20. The operation knob B30 has a cylindrical peripheral wall B31. The operation knob B30 rotates around the fixed display B60. The operation knob B30 has a front end surface B34 extending substantially parallel to the fixed display B60. The illumination light source B40 and the light guiding body B20 are provided on a reverse side of the fixed display B60.
The fixed display B60 is provided with a display marking B62 indicating air conditioner temperature or the like. The front end surface B34 of the operation knob B30 is provided with a pointer display B36 indicating a rotation position of the operation knob B30. The light guiding body B20 guides light from the illumination light source B40 to the fixed display B60 and the front end surface B34 of the operation knob B30. The light from the illumination light source B40 illuminates the display marking B62 and the pointer display B36.
Specifically, the light guiding body B20 is provided inside the operation knob B30. The light guiding body B20 has a reversed cone shape. A through hole B20a is provided at a vertex of the light guiding body B20. The through hole B20a and the illumination light source B40 face each other. A bottom surface B20b of the light guiding body B20 and the pointer display B36 face each other. An interior portion B22 of a wall defining a reversed cone shape of the light guiding body B20 acts as a central light guiding path. The light from the illumination light source B40 passes through the through hole B20a and enters the interior portion B22 of the light guiding body B20. The interior portion B22 of the light guiding body B20 guides the light from the illumination light source B40 toward a fixed display B60 side. Further, a wall interior B24 of the light guiding body B20 acts as a side light guiding path. The wall interior B24 of the light guiding body B20 guides the light from the illumination light source B40 to the front end surface B34 of the operation knob B30.
In the operation device having the rotationally operated operation knob described above, it is desirable that the peripheral wall of the operation knob is illuminated along a circumferential direction in order to indicate a position of the operation knob or from a viewpoint of design.
As a configuration in which such illumination is performed in the operation device B10 disclosed in the Patent Literature 1, for example, a configuration may be considered in which the bottom surface B20b of the light guiding body B20 faces the peripheral wall B31 of the operation knob B30. In this configuration, the wall interior B24 of the light guiding body B20 guides the illumination light source B40 to the peripheral wall B31 of the operation knob B30. In this configuration, however, the light needs to pass through the wall interior B24 of the light guiding body B20. Therefore, the wall of the light guiding body B20 of this configuration becomes thick and the thick-walled light guiding body B20 is provided along the circumferential direction of the operation knob B30, which results in an increase in weight and cost.